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Space debris is the collection of nonfunctioning man-made objects orbiting in space. There are various forms of this waste, including old satellites, spent rocket stages, decaying spacecraft and launch vehicles, and even tiny flecks of paint released by thermal stress or small particle fragments from disintegration, erosion, and collisions.
Over 20,000 objects are currently floating around the planet that are large enough to be tracked, but only less than 2,000 of those are operating satellites. What this means is that most of what is orbiting up there is waste.
Even more unfortunately, only large orbital debris, greater than 10 cm, are tracked routinely, but objects that are too small to be tracked can also cause immense damage to satellites. An object the size of a bullet can cause significant damage to a satellite, or even kill it, if it hits the wrong place.
This junk flying around our planet is typically ten to twenty times faster than the speed of a bullet, at around 7.5 kilometers per second. As a result, space debris poses immense danger to satellites in low Earth orbit.
Satellite technology is a necessary means for communications, navigation, utilities, and services. If a satellite is destroyed from space debris, it may take years and hundreds of millions of dollars to restore its service. As a result, space debris affects each and every one of us who utilize modern technology.
BTRtoday speaks with Dr. William Ailor, who has been studying the physics of spacecraft and space debris reentering the Earth’s atmosphere for over 40 years and currently serves as the principal engineer for the Center for Orbital and Reentry Debris Studies (CORDS) at The Aerospace Corporation.
Ailor says that the biggest problem is the collision of two large objects. “We had a collision with an Iridium satellite and a dead Russian satellite a few years ago that created around 3,000 tracked objects—those were fairly large objects— and a large cloud of smaller stuff that was also a threat.”
After this debris has formed, it stays in space for a very long time, depending on the altitude where it was born and the event that caused it.
“If it’s a low Earth orbit, roughly where the space station is, around 450km up, things will come down within a year or two. The higher up you go, the longer stuff will stay up there. If you get up to the Iridium Satellites, which is around 780km, the lifetime of something that orbits there is over 1000 years,” Ailor explains.
The junk poses the greatest danger to satellites in low Earth orbit, where debris can slam into a spacecraft at a combined speed of more than 30,000 mph. This area of space is where most military satellites are deployed.
Even the tiniest pieces of debris have enough energy to damage or destroy these military satellites. As a result, the mass space junk floating around the planet could lead to a political row or armed conflict.
Since humans put this garbage up there, it should be our responsibility to take necessary precautions and keep space clean to avoid further collisions. “It’s kind of like trash on earth, where you don’t think about it for such a long time then all of a sudden you’re like, wait a minute we’re leaving a mess here we need to clean it up,” Ailor compares.
Unfortunately, there is no simple solution to cleaning floating garbage as it would be very expensive and take many years. The best choice would be to not leave more objects in orbit once they are no longer useful.
Ailor explains that back in the old days, satellites would simply die in space. Since they might have some propellant remaining on board, after a few years the propellent on the tanks might explode for some reason or another, and that would create a large cloud of debris. As a result, the requirements on how to get rid of old satellites and rockets are much stricter nowadays.
There are both controlled and uncontrolled re-entries. Many large objects just stay in orbit even after their mission is completed. If they are deemed too hazardous they are required to be de-orbited. This process requires getting close to the object at its same speed, attaching to it, and moving it into a lower orbit usually into the ocean.
“They have to be sent down, under control, into the atmosphere so they burn in a particular place where they won’t hurt anybody,” Ailor explains.
However, if the object still has a propellant on-board, there is an explosion risk. There is also the concern of property rights as nations cannot grab a satellite or rocket that belongs to another country without their permission.
The other solution is to keep track of what is up there no matter who it belongs to. Realistically, there is no easy way to control or track the smaller objects.
As for the 20,000 objects or so that are large enough to track, if you know where they are, you can move them or move out of their way.
“Those things that explode or collide are things that we put up there so in theory we should know what they’re up to,” Ailor agrees.
The Aerospace Corporation provide links to predicted reentry times for larger waste focusing on objects which are reentering as a result of natural orbit decay, rather than objects which are intentionally de-orbited.
There is some concern about uncontrolled orbital junk returning to earth, however. The hazard to people or property from reentering space hardware is unlikely and there are no known reports of death from such events.
Only one person is known to have been touched by a piece of space debris, and she was simply brushed on the shoulder, completely uninjured, while walking early in the morning. The risk that an individual will be injured from fallen debris is estimated to be less than one in one trillion.
Most debris does not survive the severe heating that occurs during reentry. Components that do survive are typically slowed down by the time they reach Earth, and will fall straight down at a terminal velocity depending on the object itself.
“Things come down very slowly and basically the reason they come down is because of atmospheric drag, so there’s just a little bit of air up there, but not much,” Ailor explains. “The amount of air decreases rapidly as you start going up in altitude. Those few molecules that exist at these low altitudes will slow down objects over an increasingly long period of time depending on the altitude.”
Luckily, waste usually falls into the oceans, other bodies of water, or sparsely populated areas like the Canadian Tundra, the Australian Outback, or Siberia in the Russian Federation. During the past 50 years an average of one cataloged piece of debris fell back to Earth each day.
“We have say, 50 to 80 large objects a year that come down and potentially land some debris on the planet. We’ve recovered a few large items like that and we do research on them here,” Ailor says.
Ailor details that the biggest object The Aerospace Corporation has uncovered was an object about 250 lbs found sitting next to a farmer’s house in Texas. While no damage resulted, Ailor jokes, “The farmer wasn’t too happy about that.”